AT&T 2500 series, 7500 series, 7100 series, 7200 series 22DISTRIBUTED Communications System DCS

6-22DISTRIBUTED COMMUNICATIONS SYSTEM (DCS)

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A

Call goes over this tie trunk.

C

DCIU or PI

Link i, channel j

All links and channels between here used up , let’s say, so take detour via B to find

a route to C.

Message for call takes this route

DCIU or PI

Link m, channel n

DCIU or PI

B

Since some delay is introduced if the message takes a detour like this, however, the number of hops is not unlimited. If too many hops are used to get the message to the destination, the last digit of the call will arrive at the system at the other end of the trunk group and the call will be sent either to a station or on to another node without the message data to make the call transparent. The number of hops the message can take and still get to the terminating system on time depends on factors such as traffic and distance detoured. A maximum of two hops is usually safe, but in some situations two hops might be too many. More than two hops is not officially supported by AT&T.

DCS messages cannot traverse the AT&T Software-Defined Network (SDN).

In designing a DCS cluster that includes a System 75 R1V2 or System 75 XE R1V2 switch, remember that these switches can serve only as endpoints in a DCS cluster, but not as tandem nodes. Because these switches cannot tandem a DCS call from another node in the DCS cluster, in clusters consisting only of System 75 (R1V2) or System 75 XE switches, a tie trunk group must interconnect every pair of nodes to provide voice communications between all the switches.

Note that when a DCS cluster involves connections between a System 85, Generic 2, or DIMENSION and another System 85, Generic 2, or DIMENSION PBXs, an economical alternative to incorporating two DSUs in the DCIU connections is the 105A Isolating Data Interface (IDI). A 105A IDI provides ground isolation for up to 400 feet cable distance between switch processors. It operates automatically with the synchronous data speed selected for the DCIU. It also takes the timing from the DCIU as the controlling timing source. There are no option settings on the 105A IDI.

In designing the intracluster routing for DCS with AAR (the PNA, UDP, or ETN [Standard Network] package), it is recommended not to design the tie trunks with overflow to off-net facilities, since these facilities do not support DCS. Because calls using public network facilities lose DCS transparency, the inconsistency of feature operation between off-net and on-net calls may confuse users.